Vibrations and/or shocks can excite resonant frequencies in structures. Damping and/or isolation can be used to reduce the vibration and shock effects.
Applications where vibration and shock control are particularly important include disk drive applications, actuator voice coil motor applications, computer shock isolation applications, car applications, shock isolator applications for drawers or doors, and the like.
As a specific example, resonant vibrations or shocks in a disk drive can be caused by the read-write actuator voice coil motor assembly. An actuator is used in a disk drive to very quickly and precisely position the read/write element over the data track of a spinning disk. The actuator voice-coil motor design most often used to position the transducer can often generate vibrations that lead to excessive acoustical noise that is irritating to users of the disk drive. These vibrations can also impair the positioning or stability of the read-write transducer over the desired data track, thus reducing the drive's performance.
FIG. 1 illustrates a partial exploded view of a disk drive with only a few key features shown for clarity. FIG. 1 shows top cover 2, a bottom cover 4, and a top magnetic plate of the voice coil motor 6. A damper which would be used to damp vibrations within the disk drive could be positioned on the top magnetic plate of the voice coil motor 6. The damper location is indicated as 8. A more detailed description of a disk drive and actuator voice coil motor is found in U.S. Pat. No. 5,224,000.
One method of damping such an actuator is to use a damper which is a die cut part of damping material that is placed in key areas which experience vibration to add damping to the actuator motor assembly. (See FIG. 2 where the die cut part of damping material is represented by 10, the top cover of the disk drive is 2, and the top magnetic plate of the voice coil motor is 6.) Typically, the damper is placed between a portion of the motor assembly and an outer surface, such as the drive's cover or base. Known dampers often use a damping material with a tacky surface associated with the polymer that can make their use difficult.
Known die cut dampers are typically from 0.025 mm (1 mil) thick to over 3.81 mm (150 mils) thick. These die cut dampers have essentially flat top and bottom surfaces and straight die cut side edges that are essentially perpendicular to the top and bottom surfaces of the damper. The vibration damper may optionally have a polymeric film layer, for example, a die cut piece of polyester or polyethylene film, attached to the damper with a pressure sensitive adhesive. The add on polymeric film covers only the top portion of the flat top damper. This polymeric film layer can be the same size as the damper top surface area or extend past the top surface edges. (See FIGS. 2a and 2b, respectively. In FIG. 2a the polyethylene film is 16, the pressure sensitive adhesive is 14, the damping material is 12, the disk drive cover is 2, and the top magnetic plate of the voice coil motor is 6. In FIG. 2b the polyethylene film is 22, the pressure sensitive adhesive is 20, the damping material is 18, the disk drive cover is 2, and the top magnetic plate of the voice coil motor is 6.) Neither the surface of the film in contact with the damper, nor the damper surface with which the film is in contact, is three dimensional. The films do not offer any significant damping benefit as compared to the damping material and the main benefit the film does provide is to provide a tack-free surface on a single flat surface of the damper that will not bond to other surfaces it contacts.
Two-piece "damping" constructions that use a damper and a separate die cut film part have been used in disk drive systems where a damper (a die cut section of damping polymer) has a film (a polyethylene polymeric film with a pressure sensitive adhesive on one side) attached to a surface opposite from that which the damper is placed on, such that when the drive is assembled, the damper and film are in contact (See FIG. 2c, wherein the polyethylene polymeric film is 26, the pressure sensitive adhesive is 28, the damping polymer is 24, the top cover of the disk drive is 2, and the top magnetic plate of the voice coil motor is 6). The film provides a surface to which the damper will have a fairly weak bond so that the drive can be easily opened and reworked. The surface of this film in contact with the damper is not three dimensional, nor does it contact a three dimensional surface of the damper.